Instructions are in the homepage of the app itself, but here is a tutorial, please pay attention.]

I have tested this on an iPhone 3GS, iPhone 4 and iPhone 4S. All work perfectly and beautiful. There are some pointers to be noted.

I RECOMMEND PATCHING COMMCENTER AS IT WILL ENSURE YOUR APN SETTINGS STICK ON REBOOT

Installation

Add cydia.bbyscroopy.com to your cydia sources.

Search for i5MMS on cydia and select install, it will install some requirements in order for i5MMS to work.

Respring once installation is complete and open i5MMS from SpringBoard.

Click on the middle tab called 'i5MMS' and you will click either T-Mobile USA, Straight Talk or Simple Mobile.

For T-Mobile you will tap on any of the 5 options and cycle though each one of them until your iPhone is working and select 'Apply Settings'.

For Simple Mobile and Straight Talk simply tap 'Apply Settings'.

Device will respring, open 'Settings' app.

Go to General>Network. Here you may disable '3G' and enable 'Data Roaming'.

Continue on to 'Cellular Data Network' and scroll to the bottom and you will tap 'Reset Settings' TWICE. (2)

If Internet Tethering option is not available it may not be enabled for you, best option would be to a clean restore, else navigate all the way back to the first screen called 'Settings'.

Go to 'Facetime' preferences and toggle it to On.

Now go to 'Messages' preferences and toggle it On.

Now navigate to General>Network you should now be able to enable 'Personal Hotspot'.

You are done, now you may add T-Mobile carrier logos, and patch CommCenter.

NOTE

The button called 'Fix' in the Facetime + iMessage Fix menu will provide a fix but you will need to toggle Facetime and iMessage OFF and ON.
I have also added a new button called 'Reset' click this to erase any carrier settings previously set to be able to start over and perhaps fix a problem.

Help

If you need any help or are running into problems go to the 'Diagnostics' tab on bottom and press the button 'Run Diagnostics' this will send me a diagnostic report and enable me to help you out better.

Same here :'(... I recently had to upgrade to its 5.1.1 on my iPhone 4S due to the fact that I got the spinning wheel of death.... But since it says it works for 5.1.1 I figured it wouldn't matter... But every time I download I open the app.. I get the respring wheel but still on the app. Then it crashes... This happens on every attempt to launch the app... Like I said I'm on iPhone 4S 5.1.1 with gevey ultra S sim unlocked.. Please fix and once again Thanks In Advance

I'm having some problems ... After I do the enable features for iMessage and FaceTime... I go to settings and enable both.. Then it says waiting for activation.. After a while it says actuation unsuccessful please try again.. Plz help
THANKS in Advance

Thanks BbyScroopy. MMS works great!! Comm Center patch does not seems to work, I have 4s with Gevey ultra s, jail broke, Yes, I did turn the 3 G OFF, After the patch, I did the enquiry for for SMS center by dial the #7xxx command#, it still return 7. Someone at T-Mobile forum, posted a solution, after setting the sms center with dialer, it will prompt success, but the center number is missing, it show a button for Dismiss, do not hit Dismiss button, power down, take out the gevey card, power up, reinsert Gevey card, SMS start working, did enquiry again, it shows 206,xxx,xxxx call center number for T-Mobile. It is a pain. so is everything about iphone with T-Mobile. Gevey ultra is kind flaky at times as well.